In general, a reciprocating compressor uses a driving motor to reciprocate a piston in a cylinder and sucks, compresses and discharges refrigerant by the reciprocating movement.
FIG. 1 is a view of a part of a conventional reciprocating compressor. As illustrated in FIG. 1, refrigerant is sucked from a suction pipe 2 outside a shell 1 into a suction muffler 10 inside the shell 1. After its vibration and noise are reduced, the refrigerant is transferred to and compressed in a compression mechanism (not shown) of the compressor.
The compressors are divided into an indirect-suction type and a direct suction type according to a suction passage of refrigerant, which is determined by a connection type of the suction pipe 2 and the suction muffler 10.
The indirect-suction type compressor is configured such that a predetermined spacing is defined between the suction pipe 2 and the suction muffler 10. A front end portion of the suction pipe 2 inside the shell 1 is not connected directly to the suction muffler 10 but positioned at the front of an inlet port 10h of the suction muffler 10. Therefore, the indirect-suction type compressor improves vibration and noise performance because wave energy produced by the behavior of a suction valve (not shown) is reduced through the inner volume of the shell 1 so as not to affect the suction pipe 2. However, it degrades cooling capability and efficiency because the sucked refrigerant is influenced by the compressed refrigerant.
Accordingly, recently, the direct-suction type compressor has been widely used to overcome the refrigerant insulation problem of the indirect-suction type compressor. That is, the direct-suction type compressor is configured such that the suction pipe 2 and the suction muffler 10 are connected directly to each other, which not only prevents heat transfer between the heated refrigerant and the sucked refrigerant inside the shell 1 but also prevents re-suction. Therefore, the direct-suction type compressor can increase the specific volume of the sucked refrigerant and thus improve freezing efficiency.
FIG. 2 is a view of an example of the suction muffler for the conventional reciprocating compressor.
As illustrated in FIGS. 1 and 2, the suction muffler 10 includes a main body 11 defining a space for reducing noise, and a connection member 12 for guiding refrigerant to be sucked into the main body 11.
The main body 11 is generally formed by coupling an upper main body 11a to a lower main body 11b. A discharge portion 13 is provided at the upper side of the upper main body 11a, the inlet port 10h through which the refrigerant is sucked is formed at one side of the lower main body 11b, and the connection member 12 is connected to the inlet port 10h. 
A part of the connection member 12 connected to the inlet port 10h has a smaller diameter than the opposite part thereof to easily transfer the refrigerant into the compressor. That is, the connection member 12 is generally formed in the shape of a funnel. In addition, the connection member 12 is mostly made of an elastic-deformable material and installed inside the shell 1 to connect the suction pipe 2 outside the shell 1 to the main body 11 inside the shell 1.
The direct-suction type compressor, in which the suction muffler 10 is connected directly to the suction pipe 2, cannot secure a buffering space for reducing wave energy produced by vibration generated by the compression mechanism or the behavior of the suction valve. Therefore, the resulting shock is transferred to the suction pipe 2 as it is.
As compared with the indirect-suction type compressor, the direct-suction type compressor is advantageous in terms of freezing efficiency but disadvantageous in terms of noise. That is, when this compressor is applied to a product such as a refrigerator, pressure pulsation transferred through the suction pipe of the compressor and vibration and shock caused by the opening and closing of the suction valve are transferred to the entire product and operated as a noise source.
Moreover, a refrigerant suction passage may be narrowed to reduce noise in the compressor. This serves as a flow resistance reducing flow efficiency, and thus degrades efficiency of the entire product using the compressor.